Milk from a representative sample of the Belgian dairy cattle composed of 797 Black and White and 226 Red and White cows was collected at the milk station in the State Agricultural Research Station in Gembloux. These samples were phenotyped for as1 -casein, p-casein, K-casein and p-lactoglobulin by isoelectric focusing on an acrylamide gel. Milk, fat and protein productions were available on these cows. Linkage disequilibrium of the casein loci and the relationship between milk protein genotypes and production traits (milk yield, fat yield, protein yield, fat percentage, protein percentage) was investigated. Gene frequencies were similar to those found in other studies. Linkage was confirmed between p-CN and k-CN , and also between the as1-CN and p-CN loci for the two breeds. In the Belgian Black and White, linkage between as1-CN and k-CN was confirmed as well. As in other studies, casein haplotypes (as-|-, p- and k-CN) BBB and CA3A occurred in the population more often than would be expected from a random combination of the alleles. Animal model analysis of the production data indicated a significant positive effect of the BB genotype of the k-CN on protein percentage in the Red and White breed. In the Black and White breed, the AA genotype of the p-LG genotype had a negative impact on fat production compared to AB and BB genotypes, while the BB genotype of the asi-CN had a positive effect on fat yield, and the At A 1 genotype of the p-CN had a negative effect on milk production, and a positive one on fat percentage (significant when compared to A1A 2 and to A2A2).

F. P Farnir, J. Laloux, M. Georges, Pascale Le Roy, J. M Beduin

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 19. Selection and quantitative genetics; growth; reproduction; lactation; fish; fiber; meat., , 337–340, 1994
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